Gerald Moan of Tuscon, Ariz., will head the party until a new chairman is selected at its summer convention, Choate said.

Choate, the 1996 Reform Party vice presidential nominee, said in a telephone interview with The Associated Press that the party is united after months of wrangling, thus his departure will not be unsettling. Former Republican presidential candidate Pat Buchanan, recruited to the party by Choate, is the leading contender for the third-party nomination.

``I think we've got things in good shape,'' Choate said. ``I think we're on a glide path to the convention.''

Choate announced his resignation in a letter to the party's executive council. The letter noted ``an illness in our family that requires the immediate attention of my wife and me.'' He said in an interview the illness was a private matter.

Choate's claim to the job was challenged this year by rivals within the party, but a federal judge upheld his chairmanship. His first order of business was to try to soothe internal strife.

Choate, 59, is no stranger to Washington or party politics. He was party founder Ross Perot's running mate in 1996 when the two got 8 percent of the national vote - enough to secure $15 million in public funding this year for the party's convention and general election.

Four years earlier, though he was not on the ticket, he helped Perot secure 18 percent of the vote, a significant chunk that may well have decided the election in Bill Clinton's favor.

Choate grew up in Red Oak, Texas, picking cotton on his father's farm. After earning a doctorate from the University of Oklahoma in 1969, he moved to Washington to work for the Commerce Department. He now lives on his own farm in Washington, Va., with his wife, Kay.

He has advised his friend Buchanan on foreign policy, and he coached Perot before a 1993 debate with Gore over the North American Free Trade Agreement. Choate argues that open markets have cost millions of American jobs by forcing U.S. workers to compete with cheap overseas labor.